1. Field of the Invention
The present invention relates generally to improvements in seat belt retractors, and more particularly to seat belt retractors which are suitable for use in motor vehicles.
2. Brief Description of the Prior Art
One form of a seat belt retractor in use today employs a ratchet wheel on which the seat belt is wound. A metal lock bar is actuated by an inertia weight for insertion into the ratchet wheel upon sudden deceleration of the vehicle. The ratchet wheel, when engaged by the lock bar is prevented from rotation which would allow a pay-out of the seat belt, thereby securing the occupant of a vehicle in the event of a collision or other sudden vehicle deceleration. Teeth on the ratchet wheel engage the lock bar and hold the lock bar in its locking position because of the rake on the ratchet teeth.
A number of approaches have been taken to assure that as the locking member is advanced towards a locking position, it will reach that position even though it may hit the tip of a ratchet tooth and thereby not enter immediately between ratchet teeth where it will block further protraction of the seat belt. For example, U.S. Pat. No. 4,166,592 issued Sept. 4, 1979, provides an inertia weight carried on a spring arm, made either from a coiled spring or a plastic rod. This design has been effective in reducing the delayed blocking of the ratchet wheel during a time when the locking member would otherwise "bounce back," but for the resilient rod. U.S. Pat. No. 3,930,622 issued Jan. 6, 1976 also discloses a first embodiment having a resilient rod or stem made from a coil spring. In another embodiment, a conventional, nonresilient weight engages a leaf spring connected to a locking arm. Energy is stored in the leaf spring, which is attached to one end of the arm. Construction of these weights is somewhat complicated, requiring multiple steps for their assembly. It is desired to provide the same resilient biasing of the locking member without requiring an inertia weight assembled from a variety of materials and components.
In order to assure the timed movement of the locking bar into the space between adjacent ratchet wheel teeth, U.S. Pat. No. 4,603,819 provides a timing gear secured to one face of a main ratchet wheel, such as the ratchet wheels described above. In comparison to the main ratchet wheel, the timing gear has teeth that are longer and more pointed, having a smaller included angle at their tip. A pawl-like pick member activated by the weight is pivotally mounted on the retractor frame for inter-engagement with the teeth of the timing gear. The pick forms part of a body member which also includes a bar-engaging portion. Upon engagement of the pick with the timing gear, the bar engaging portion lifts the locking bar into engagement with the main ratchet wheel. Due to the shape of the timing gear teeth and their position and size relative to the teeth of the main ratchet wheel, they provide a timing function which ensures that the locking member does not engage the tip of the main ratchet wheel tooth, but rather is always directed between the teeth of that wheel. While generally satisfactory, more parts are required, and proper alignment during fabrication must now be provided not only for the main ratchet wheel and the locking member, but also for the pick and the timing gear. Any reduction in parts or labor needed to fabricate a retractor can have a tremendous effect on price and profitability, considering the economies of scale attendant in the automotive industry.
In constructing safety belt retractor mechanisms on a high-volume mass production basis, a number of steps are taken to assure that the retractor always functions properly despite any tolerance build-ups or variations in parts. For example, the relative spacing between the head of the weight and the locking member is often adjusted to assure the necessary travel of the locking member necessary to accomplish a locking engagement in the event of a sudden deceleration. Typically, the locking member is pivoted at one end and its opposing free end is swung into engagement with the ratchet wheel by the head of the weight which engages the locking member at a point intermediate its ends. Thus, an undesired spacing between the head of the weight and the portion of the locking member near its pivoted end could be amplified at the free end of the locking member. The effective locking operation of the retractor is closely monitored during assembly on a production line. Adjustments in the spacing of these pendulum-type inertia weights have been made by applying shim members to either the head of the weight or more often to the locking member to assure that the retractor will lock if it does not lock on its first test operation. A fairly large number of different sized shims is required, and the alignment procedure of selecting and applying a shim member slows the high volume mass production assembly of the retractor.
Other types of inertia weight arrangements, such as the "toppling-type" or "standing man-type" have had different adjusting arrangements. For example, U.S. Pat. No. 3,990,651 issued Nov. 9, 1976, discloses a plastic pin beneath a toppling weight. The plastic pin rides in a guide channel, and has a shaft protruding beyond the guide channel. When the proper position of the weight is achieved during the retractor fabrication process, the pin shaft is melted, welded or otherwise joined to its guide channel, which is also made of plastic, by heat and pressure applied to the pin shaft and/or the guide channel. The plastic pin must, of course, be very accurately positioned during this process, and external apparatus is required for the positioning, as well as the application of heat and pressure.
As another example, U.S. Pat. Re. 29,095 issued Jan. 4, 1977, discloses a cone-shaped disk balanced on the sharpened tip of an arbor-like threaded shaft. The threaded shaft is locked in a mounting plate with a lock nut. The arbor-type support is not readily adaptable for other weight designs having more elaborate configurations and, in particular, is not compatible with pendulum or swinging types of weights.
In yet another example of adjusting arrangements, U.S. Pat. No. 3,999,723 issued Dec. 28, 1976, shows a pendulum-type weight. As with other pendulum weights, the head is connected to a massive end portion through a stem. However, the weight is further provided with an axial extension of the stem, projecting upwardly beyond a head from which the weight is swingingly mounted. The tip of the axial extension is positioned within a conical seat located above the weight. The conical seat is formed at one end of a threaded screw which rides within the threaded bore of a moment arm, intermediate the two ends of that moment arm. One end of the moment arm provides pivotal mounting, and the other end engages a ratchet wheel to provide a locking action in response to swinging of the weight. This arrangement is not compatible with latch arms and the like that have camming engagement with the surface of the head, one example of which is found in U.S. Pat. No. 4,447,017, issued May 8, 1984. The arrangement disclosed therein includes first and second opposed, overlapping pivotally mounted arms, the first of which overlies and rides upon the second. The second arm, in turn, has a downwardly extending projection which rides on the head of a pendulum weight, with swinging of the pendulum weight displacing both arms, in sequence.